Optical modulator robust to fabrication errors

ABSTRACT

An optical modulator includes a first arm and a second arm, each arm includes an arrangement with an equal amount of p-doped material and an equal amount of n-doped material, such that mask misalignment causes a same effect in both arms; and each arm includes a plurality of segments where electrodes connect for push-pull operation of the first arm and the second arm.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present disclosure is a national stage application of PCT PatentApplication No. PCT/US18/27239, filed on Apr. 12, 2018, which claimspriority to U.S. patent application Ser. No. 15/582,050, filed Apr. 28,2017, and now U.S. Pat. No. 10,330,961, issued Jun. 25, 2019.

BACKGROUND

An electronic component is a component that conducts, transmits,receives, generates, or otherwise uses an electrical current and/orsignal during the operation of the component. An optoelectroniccomponent is an electronic component that also uses an optical signalduring operation. An optoelectronic integrated circuit is a set ofoptoelectronic components on one small flat piece referred to as a“chip”, which is created from a batch fabrication process using a wafer.The wafer may include semiconductor material (e.g., silicon) overlaidwith additional material layers (e.g., metal, oxide, etc.) tosimultaneously fabricate a large number of the optoelectronic integratedcircuits. Subsequent to the wafer fabrication, multiple optoelectronicintegrated circuits are separated into chips for final packaging. Thelayout of the optoelectronic integrated circuit is the designedplacement of planar geometric component shapes of the optoelectronicintegrated circuit. A fabrication pattern of the optoelectronicintegrated circuit is the pattern of semiconductor, oxide, metal, orother material layers formed on a wafer, die, and/or chip based on thelayout. Misalignment is the shifting among layers in the fabricationpattern with respect to the layout.

A p-n junction is a boundary or interface between a p-type region and ann-type region of semiconductor material. The p-type region and then-type region are created by selectively doping (e.g., via an ionimplantation process, diffusion process, epitaxy process, etc.) thesemiconductor material using a p-type dopant or an n-type dopant,respectively. The fabrication pattern of the p-type region and then-type region is based on one or more lithography masks used to performthe selective doping.

A waveguide is an optoelectronic component having a physical structurethat confines and guides the propagation of an electromagnetic (EM)wave, e.g., as an optical signal. A mode is an electromagnetic (EM)field pattern in the waveguide. The fabrication pattern of the waveguidecorresponds to the physical structure and is based on one or morelithography masks used to form the physical structure.

SUMMARY

In general, in one aspect, the invention relates to an optoelectronicintegrated circuit. The optoelectronic integrated circuit includes (i) afirst back-to-back-junction component (BBJC) and a second BBJC thatconform to a first fabrication pattern, where the first BBJC includes afirst A-type p-n junction (APNJ) in series with a first B-type p-njunction (BPNJ), where the second BBJC includes a second APNJ in serieswith a second BPNJ, and (ii) an optical component conforming to a secondfabrication pattern that superimposes the first fabrication pattern,where the optical component overlaps the first APNJ and the second APNJto define a first p-type overlap region and a first n-type overlapregion, where the optical component overlaps the first BPNJ and thesecond BPNJ to define a second p-type overlap region and a second n-typeoverlap region. The APNJs and BPNJs may be identified based onoverlapping with separate arms of the optical component. The first APNJ,the first BPNJ, the second APNJ, and the second BPNJ are disposed alongrespective directions, where metal bridges may be used, such that (i)the first p-type overlap region and the second p-type region aresubstantially same size, independent of a fabrication misalignmentamount of the first fabrication pattern with respect to the secondfabrication pattern, and (ii) the first n-type overlap region and thesecond n-type region are substantially same size independent of thefabrication misalignment amount of the first fabrication pattern withrespect to the second fabrication pattern.

In general, in one aspect, the invention relates to an optical modulatorcircuit. The optical modulator circuit includes (i) a first electrodeand a second electrode that are adapted to propagate a modulatingvoltage of the optical modulator circuit, (ii) a firstback-to-back-junction component (BBJC) and a second BBJC that areconnected to the first electrode and the second electrode to receive themodulating voltage, where the first BBJC includes a first A-type p-njunction (APNJ) in series with a first B-type p-n junction (BPNJ), wherethe second BBJC includes a second APNJ in series with a second BPNJ,where the first BBJC and the second BBJC conform to a first fabricationpattern, and (iii) a first optical waveguide and a second opticalwaveguide that are adapted to propagate an optical signal of the opticalmodulator circuit, where the first optical waveguide and the secondoptical waveguide conform to a second fabrication pattern thatsuperimposes the first fabrication pattern, where the first opticalwaveguide overlaps the first APNJ and the second APNJ to define a firstp-type overlap region and a first n-type overlap region, where thesecond optical waveguide overlaps the first BPNJ and the second BPNJ todefine a second p-type overlap region and a second n-type overlapregion. The APNJs and BPNJs may be identified based on overlapping withthe first optical waveguide and second optical waveguide. The firstAPNJ, the first BPNJ, the second APNJ, and the second BPNJ are disposedalong respective directions, where metal bridges may be used, such that(i) the first p-type overlap region and the second p-type region aresubstantially same size, independent of a fabrication misalignmentamount of the first fabrication pattern with respect to the secondfabrication pattern, and (ii) the first n-type overlap region and thesecond n-type region are substantially same size independent of thefabrication misalignment amount of the first fabrication pattern withrespect to the second fabrication pattern. The respective directionsreduce an imbalance in the modulation of the optical signal using themodulating voltage from the first electrode and the second electrode.

In general, in one aspect, the invention relates to a method forfabricating an optoelectronic integrated circuit. The method includes(ii) forming a first back-to-back-junction component (BBJC) and a secondBBJC according to a first fabrication pattern, where the first BBJCincludes a first A-type p-n junction (APNJ) in series with a firstB-type p-n junction (BPNJ), where the second BBJC includes a second APNJin series with a second BPNJ, and (ii) forming an optical componentaccording to a second fabrication pattern that superimposes the firstfabrication pattern, where the optical component overlaps the first APNJand the second APNJ to define a first p-type overlap region and a firstn-type overlap region, where the optical component overlaps the firstBPNJ and the second BPNJ to define a second p-type overlap region and asecond n-type overlap region. The APNJs and BPNJs may be identifiedbased on overlapping with separate arms of the optical component. Thefirst APNJ, the first BPNJ, the second APNJ, and the second BPNJ aredisposed along respective directions, where metal bridges may be used,such that (i) the first p-type overlap region and the second p-typeregion are substantially same size independent of a fabricationmisalignment amount of the first fabrication pattern with respect to thesecond fabrication pattern, and (ii) the first n-type overlap region andthe second n-type region are substantially same size independent of thefabrication misalignment amount of the first fabrication pattern withrespect to the second fabrication pattern.

Other aspects of the invention will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1.1 and 1.2 show fabrication pattern diagrams in accordance withone or more embodiments of the invention.

FIGS. 2.1, 2.2, and 2.3 shows top view and side view diagrams inaccordance with one or more embodiments of the invention.

FIG. 3 shows a method flowchart in accordance with one or moreembodiments of the invention.

FIGS. 4, 5, 6, 7, 8, 9, 10, and 11 show examples in accordance with oneor more embodiments of the invention.

DETAILED DESCRIPTION

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency.

In the following detailed description of embodiments of the invention,numerous specific details are set forth in order to provide a morethorough understanding of the invention. However, it will be apparent toone of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-known featureshave not been described in detail to avoid unnecessarily complicatingthe description.

In the following description, any component described with regard to afigure, in various embodiments of the invention, may be equivalent toone or more like-named components described with regard to any otherfigure. For brevity, descriptions of these components will not berepeated with regard to each figure. Thus, each and every embodiment ofthe components of each figure is incorporated by reference and assumedto be optionally present within every other figure having one or morelike-named components. Additionally, in accordance with variousembodiments of the invention, any description of the components of afigure is to be interpreted as an optional embodiment which may beimplemented in addition to, in conjunction with, or in place of theembodiments described with regard to a corresponding like-namedcomponent in any other figure. In the figures, three black solidcollinear dots indicate that additional components similar to thecomponents before and after the solid collinear dots may optionallyexist.

Throughout the application, ordinal numbers (e.g., first, second, third,etc.) may be used as an adjective for an element (i.e., any noun in theapplication). The use of ordinal numbers is not to imply or create anyparticular ordering of the elements nor to limit any element to beingonly a single element unless expressly disclosed, such as by the use ofthe terms “before”, “after”, “single”, and other such terminology.Rather, the use of ordinal numbers is to distinguish between theelements. By way of an example, a first element is distinct from asecond element, and the first element may encompass more than oneelement and succeed (or precede) the second element in an ordering ofelements.

In general, embodiments of the invention provide an optoelectronicintegrated circuit having a group of back-to-back-junction components(BBJCs) overlapped by and aligned to an optical component. The BBJC aredisposed in the optoelectronic integrated circuit according to a layoutthat reduces a misalignment effect with respect to the opticalcomponent. In one or more embodiments, the BBJC and the opticalcomponent form two arms of an optical modulator. The p-type and n-typeregions of p-n junctions are geometrically swapped between the BBJC. Forexample, each arm of the optical modulator contains substantially thesame number of (i) BBJCs having p-n junctions with p-type regions at oneside of the optical component and (ii) BBJCs having p-n junctions withp-type regions at the opposite side of the optical component.Accordingly, misalignment of the BBJCs with respect to the opticalcomponent results in substantially the same effect in both arms toreduce the misalignment effect on the optical modulator.

FIG. 1.1 shows a fabrication pattern diagram of an optoelectronicintegrated circuit (100) in accordance with one or more embodiments ofthe invention. Throughout this disclosure, the relative positions anddirections of components depicted in a fabrication pattern diagramcorrespond to physical layout positions and directions on an integratedcircuit chip or dice. In one or more embodiments of the invention, oneor more of the elements shown in FIG. 1.1 may be omitted, repeated,and/or substituted. Accordingly, embodiments of the invention should notbe considered limited to the specific arrangements of modules shown inFIG. 1.1.

As shown in FIG. 1.1, the optoelectronic integrated circuit (100)includes a sequence of back-to-back junction components (BBJCs) (e.g.,BBJC A (101), BBJC B (102), etc.) disposed in parallel and conforming toa BBJC fabrication pattern. As used herein, the BBJC fabrication patternis the pattern of semiconductor, oxide, metal, or other material layersformed on the wafer, die, and/or chip based on the layout of the BBJC.Specifically, a BBJC is an electronic component having two p-n junctionselectrically connected as either a pnnp component or a nppn component.In other words, the BBJC may have two different electrical connectionsequences (i.e., pnnp sequence or nppn sequence). The BBJC of the pnnpsequence (i.e., a pnnp component) has the n-type regions of the two p-njunctions electrically connected together. The BBJC of the nppn sequence(i.e., a nppn component) has the p-type regions of the two p-n junctionselectrically connected together.

While the electrical connection sequence of the BBJC refers to and isbased on the electrical connection of the p-n junctions, the doping typesequence of a BBJC is a physical sequence of doping types (i.e., n-typeor p-type) according to the layout of the BBJC's doped regions (i.e.,n-type region and p-type region).

The BBJC A (101) includes a p-n junction A (104) in series with a p-njunction B (105) that are formed from a physical layout sequence ofdoped regions (111), (112), (113), and (114). The doping type sequenceof the BBJC A (101) is a sequence x-y-z-w where x, y, z, and w denotethe doping types (i.e., n-type or p-type) of the doped regions (111),(112), (113), and (114), respectively. In some embodiments, anintervening non-doped region may exist between the doped regions (112)and (113). Similarly, the BBJC B (102) includes a p-n junction C (106)in series with a p-n junction D (107) that are formed from a physicallayout sequence of doped regions (115), (116), (117), and (118). Thedoping type sequence of the BBJC B (102) is a sequence q-p-r-s where q,p, r, and s denote the doping types (i.e., n-type or p-type) of thedoped regions (115), (116), (117), and (118), respectively. In someembodiments, an intervening non-doped region may exist between the dopedregions (116) and (117). For example, the doping type sequence of theBBJC A (101) and/or BBJC B (102) may be n-p-n-p, p-n-n-p, n-p-p-n,p-n-p-n.

In one or more embodiments, the doped regions (111), (112), (113),(114), (115), (116), (117), and (118) are electrically interconnected(not explicitly shown) via contiguous same-type doped regions and/or viametal bridges to form respective pnnp or nppn component. In particular,the doping type sequence and the electrical connection sequence relateto the fabrication pattern of the BBJC A (101) and the BBJC B (102)(more particularly, of the doped regions (111), (112), (113), (114),(115), (116), (117), and (118)), which is based on one or morelithographic masks used to perform the selective doping for the BBJC A(101) and the BBJC B (102). Various doping type sequences and electricalconnection sequences of the doped regions (111), (112), (113), (114),(115), (116), (117), and (118) are described in reference to FIGS.2.1-2.3 below.

Further, as shown in FIG. 1.1, the optoelectronic integrated circuit(100) includes an optical component (103) that conforms to an opticalcomponent fabrication pattern. As used herein, the optical componentfabrication pattern is the pattern of semiconductor, oxide, metal, orother material layers formed on the wafer, die, and/or chip based on thelayout of the optical component. In particular, the fabrication patternof the optical component (103) superimposes the fabrication pattern ofthe BBJC A (101) and the BBJC B (102). The two fabrication patterns havea misalignment (302) with respect to a division line (301) of theoptical component (103). In particular, the p-n junction B (105) and p-njunction D (107) are designed to coincide with the division line (301)according to the layout of the optoelectronic integrated circuit (100).For example, the division line (301) may be specified by a circuitdesigner in the layout of the optoelectronic integrated circuit (100) todivide the optical component (103) into portions overlapped by dopingregions of the opposite types. During fabrication, the misalignment(302) results from a shifting between the aforementioned lithographicmasks.

Depending on which side an overlap region is with respect to themisalignment (302) or the misaligned p-n junction, the misalignment(302) causes the overlap of the optical component (103) and the dopedregions to have different sizes than what is specified by the circuitdesigner. For example, the optical component (103) (or the fabricationpattern thereof) overlaps the doped regions (111) and (112) (or thefabrication pattern thereof) to define two different-size andopposite-type overlap regions (highlighted) separated by the p-njunction A (104). Similarly, the optical component (103) (or thefabrication pattern thereof) overlaps the doped regions (113) and (114)(or the fabrication pattern thereof) to define two different-size andopposite-type overlap regions (highlighted) separated by the p-njunction B (105). The different-size and opposite-type overlap regionsin the BBJC A (101) may result in an overlap region size imbalancebetween the two p-n junctions (i.e., p-n junction A (104), p-n junctionB (105)) for either the p-type region or the n-type region. The overlapregions of the BBJC B (102) may also result in another overlap regionsize imbalances as the BBJC A (101).

In one or more embodiments, the p-n junction A (104), p-n junction B(105), p-n junction C (106), and p-n junction D (107) are disposed alongrespective directions such that (i) the combined p-type overlap regionof the p-n junction A (104) and p-n junction C (106) has a substantiallysame size as the combined p-type overlap region of the p-n junction B(105) and p-n junction D (107) independent of the misalignment (302),and (ii) the combined n-type overlap region of the p-n junction A (104)and p-n junction C (106) has a substantially same size as the combinedn-type overlap region of the p-n junction B (105) and p-n junction D(107) independent of the misalignment (302). As used herein, a directionof a p-n junction is the geometric direction from the p-type region tothe n-type region according to the layout of the doped regions.

In one or more embodiments, the optical component (103) includes twosections, referred to as an arm A and an arm B. For example, one sectionoverlaps the p-n junction A (104) and p-n junction C (106) while anothersection overlaps the p-n junction B (105) and p-n junction D (107). Inthis context, the p-n junction A (104) and p-n junction C (106) arereferred to as A-type p-n junctions (APNJs) while the p-n junction B(105) and p-n junction D (107) are referred to B-type p-n junctions(BPNJs). In other words, the APNJ is an p-n junction overlapped by thearm A while the BPNJ is an p-n junction overlapped by the arm B.Specifically, the p-n junction A (104) and p-n junction C (106) form afirst group (i.e., A-type) of p-n junctions while the p-n junction B(105) and p-n junction D (107) form a second group (i.e., B-type) of p-njunctions.

Various directions of the p-n junction A (104), p-n junction B (105),p-n junction C (106), and p-n junction D (107) to reduce the effect ofmisalignment induced overlap region size imbalance, in particular alongthe cross section A (120) and cross section B (121), are described inreference to FIGS. 2.1-2.3 below.

FIG. 1.2 shows a fabrication pattern diagram of an optical modulatorcircuit (200) in accordance with one or more embodiments of theinvention. In one or more embodiments of the invention, one or more ofthe elements shown in FIG. 1.2 may be omitted, repeated, and/orsubstituted. Accordingly, embodiments of the invention should not beconsidered limited to the specific arrangements of modules shown in FIG.1.2.

As shown in FIG. 1.2, the optical modulator circuit (200) is anintegrated circuit that is a superset of the optoelectronic integratedcircuit (100) with additional components denoted according to the legend(210). Although not explicitly shown, in one or more embodiments, aradio frequency (RF) termination is connected to the electrodes on theopposite end from the bias voltages. Specifically, a common connection(213) to all p-n junctions of the BBJCs (e.g., BBJC A (101), BBJC B(102), etc.)) is adapted to receive a bias voltage for setting updepletion regions of the p-n junctions. The two ends of each BBJC (e.g.,BBJC A (101), BBJC B (102), etc.)) are connected to an electrode A andelectrode B, respectively, that are adapted to receive a modulatingvoltage. In particular, p-n junctions that overlap an arm A (211) of thesilicon waveguide are APNJs. Similarly, p-n junctions that overlap anarm B (212) of the silicon waveguide are BPNJs. The arm A (211) and armB (212) correspond to the two sections of the optical component (103)depicted in FIG. 1.1 above. Specific connections from the APNJs andBPNJs to the electrode A and electrode B are not explicitly shown inFIG. 1.2. Various electrode connection configurations for the APNJs andBPNJs are described in reference to FIGS. 2.1-11 below. The modulatingvoltage corresponds to input data (i.e., Data IN) which modulates thedepletion region widths of the APNJs and BPNJs. The free carrier densityin the p-n junctions being modulated translates into a modulation of therefractive index of the p-n junctions and to a phase modulation of anoptical signal propagating from LI to LO along the arm A (211) and arm B(212) of the silicon waveguide. By merging the arm A (211) and arm B(212) in an interferometer configuration, the optical signal output(i.e., LO) is encoded with information from the input data (i.e., DataIN).

As noted above, the p-n junctions in the APNJs and BPNJs are disposed inrespective directions to reduce the effect of misalignment inducedoverlap region size imbalance in the optoelectronic integrated circuit(100) and an imbalance in the modulation efficiency between the firstgroup (i.e., A-type) and second group (i.e., B-type) of p-n junctions(i.e., APNJs and BPNJs). For a balanced operation of the opticalmodulator circuit (200), the combined p-type overlap region of the firstgroup p-n junctions (i.e., APNJs) has a substantially same size as thecombined p-type overlap region of the second group p-n junctions (i.e.,BPNJs) independent of the misalignment (302). In addition, the combinedn-type overlap region of the first group p-n junctions (i.e., APNJs) hasa substantially same size as the combined n-type overlap region of thesecond group p-n junctions (i.e., BPNJs) independent of the misalignment(302). In other words, the respective directions of the first group andsecond group p-n junctions (i.e., APNJs and BPNJs) are designated in thelayout of the optical modulator circuit (200) to reduce the misalignmentinduced imbalance resulting from modulating the optical signal using themodulating voltage from the electrode A and electrode B.

In one or more embodiments, the optical modulator circuit (200) isfabricated in silicon as a Mach-Zehnder (MZ) modulator used for lightmodulation in optical telecommunication applications. Unlike lithiumniobate or other material that have electro-optic properties suitablefor optical signal modulation, modulation in silicon waveguides isachieved based on the dependency of the refractive index to the freecarrier density in the depletion region. Accordingly, by constructing ap-n junction within an optical waveguide and by applying a time-varyingreverse voltage, the depletion region of the p-n junction (inparticular, the free carrier density) may be modulated, leading to amodulation of the refractive index. In one or more embodiments, thedirect current (DC) portion of the time-varying reverse voltage issupplied by the bias voltage while the alternating current (AC) portionof the time-varying reverse voltage is supplied by the modulatingvoltage.

In the MZ modulator, the presence of free carriers decreases therefractive index for both electrons and holes. The p-n junction islocated in the silicon waveguide and modulation of the depletion widthof this p-n junction affects an overlapping portion of the optical modepropagating in the waveguide. Accurate positions of the p-n junctionwithin the optical waveguide improves the modulation performance. P-typeand n-type dopants are implanted at proper locations defined bylithographic masks aligned over the already defined waveguides. Forexample, the alignment, performed over multiple optoelectronicintegrated circuits of the entire wafer, may have an accuracy ofapproximately 50 nm (nanometer) while the waveguide may have a width ofapproximately 400 to 500 nm. Compared to the width of the waveguide, thealignment error may not be negligible and may therefore cause asignificant variation in the modulation efficiency across the wafer.

As an example, each arm of the MZ modulator (e.g., arm A (211), arm B(212)) with the associated electrode may be several mm (millimeter) longto produce the designed phase modulation amplitude. For operation athigh frequency (i.e. 10's of GHz (giga-hertz)), the MZ modulator armsare implemented using radio frequency (RF) traveling-wave electrodesacting as RF transmission lines. The traveling-wave RF electrodes areelongated electrodes connected to p-n junctions for transmitting themodulation voltage(s). By way of this connection, the capacitance of thep-n junctions adds to the capacitance of the elongated electrodes, whichis referred to as the capacitance loading. The capacitance loadingresults in a characteristic impedance matching with respect to the inputdriver circuit. In addition, the capacitance loading results in a groupvelocity matching with respect to the optical waves propagating in theoptical waveguides.

As shown in FIG. 1.2, the p-n junctions of the MZ modulator may bedivided in segments that connect periodically (or at specific locations)to the RF traveling-wave electrodes to receive the modulation voltagefrom the input driver circuit. In other words, the RF traveling-waveelectrodes propagate the input data (i.e., Data IN) as RF traveling-waveto each p-n junction segment (i.e., one or more BBJCs) along the lengthof the MZ modulator arms. In particular, the RF traveling-wave ispropagated along the length of the arms in a push-pull operation wherethe phase changes of the optical signal in both arms are in oppositedirections. The push-pull operation reduces frequency chirp in theoptical signal output (i.e., LO) of the MZ modulator. In one or moreembodiments, a single input driver circuit is advantageously used todrive input data (i.e., Data IN) to both arms connected by BBJCs. Inparticular, the p-n junctions of the two MZ modulator arms are connectedback-to-back (i.e., with the p (or n) side of the two diodeselectrically connected together) in the SPP configuration. This circuitconfiguration is a series-push-pull (SPP) configuration.

FIGS. 2.1-2.3 show top view and side view diagrams in accordance withone or more embodiments of the invention. In the side view diagrams, thesemiconductor material layers (i.e., waveguides and doping regions) areshown in two-dimensional cross sections while the conducting layers(i.e., metal bridges and electrodes) are shown schematically as linesegments. In particular, the line segments represent electricalconnection but not physical layout. The top view and side view diagramscorrespond to the fabrication pattern of the optoelectronic integratedcircuit (100) and optical modulator circuit depicted in FIGS. 1.1 and1.2 above. In particular, the side view diagrams illustrate variouscombinations of doping type sequences, electrical connection sequences,and p-n junction directions to reduce the effect of misalignment inducedoverlap region size imbalance, in particular along the cross section A(120) and cross section B (121) depicted in FIG. 1.1 above.

FIG. 2.1 shows a side view (350) and a top view (360) of a BBJC X (324)according to the legend (300). In one or more embodiments of theinvention, the BBJC X (324) corresponds to both the BBJC A (101) andBBJC B (102) (depicted in FIGS. 1.1. and 1.2 above) that have the samedoping type sequence. Accordingly, the side view (350) corresponds toboth the cross section A (120) and the cross section B (121) depicted inFIG. 1.1 above.

As shown in FIG. 2.1, the BBJC X (324) has the doping type sequencen-p-n-p to form the APNJ (334) and BPNJ (335). In particular, the APNJ(334) and BPNJ (335) have the same p-n junction direction denoted by thearrows of the p-n junction icons. The APNJ (334) and BPNJ (335) areelectrically connected into a pnnp component (364) via the metal bridge(226). In other words, the metal bridge (226) is used to form a pnnpelectrical connection sequence. Correspondingly in FIGS. 1.1 and 1.2,the BBJC A (101) and BBJC B (102) have the same pnnp electricalconnection sequence and have the same n-p-n-p doping type sequence. Inaddition, the p-n junction A (104), p-n junction B (105), p-n junction C(106), and p-n junction D (107) are all disposed in the same direction.

Further as shown in FIG. 2.1, the electrode A (303), electrode B (304),waveguide A (311), waveguide B (312), division line (301), andmisalignment (302) correspond respectively to the electrode A, electrodeB, arm A (211), arm B (212), division line (301), and misalignment (302)depicted in FIG. 1.1 above. In addition, the n-type overlap region (353)and p-type overlap region (354) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction A (104), asdepicted in FIG. 1.1 above. Similarly, the n-type overlap region (355)and p-type overlap region (356) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction B (105), asdepicted in FIG. 1.1 above. The different-size overlap regions merelyresult in the optical mode interacting with a larger portion of p-typematerial than n-type material on both the waveguide A (311) andwaveguide B (312). Independent of the different-size overlap regions,the optical mode still interacts with substantially same amount (e.g.,within 10% or other pre-determined amount) of p-type material on boththe waveguide A (311) and the waveguide B (312), as well as interactswith substantially same amount (e.g., within 10% or other pre-determinedamount) of n-type material on both the waveguide A (311) and thewaveguide B (312). Accordingly, the same directions of the APNJs andBPNJs (i.e., p-n junction A (104), p-n junction B (105), p-n junction C(106), p-n junction D (107)) reduce the imbalance of the modulationstrength incurred in optical arms A and B.

The top view (360) shows a SPP configuration in which each segment(e.g., BBJC X (324), BBJC Y (325), etc.) contains a pnnp component witheach p-doped region on the same side of the overlapped waveguide, andwith each n-doped region on the other same side of the overlappedwaveguide, for both MZ modulator arms. The BBJC X (324) is highlightedin the top view (360) according to the legend (300). The BBJC Y (325)and BBJC X (324) are mirror image to each other (with respect to anadjoining boundary) in the top view (360) and both have the same crosssection view (350). As noted above, the impact of a misalignment of thedoped regions is substantially the same (e.g., within 10% or otherpre-determined amount) for both MZ modulator arms. According to thelegend (300), two levels of metal are used to fabricate the BBJC X(324). Specifically, the first level metal is used to electricallycontact the doped regions (using a set of appropriate vias) while thesecond level metal is used to form the electrode A (303) and electrode B(304). The metal bridges may be formed in one or more of the metallayers using another set of appropriate vias.

Although the description of FIG. 2.1 applied to FIG. 1.1 above is basedon a single doping sequence n-p-n-p for both the BBJC A (101) and BBJC B(102), the optoelectronic integrated circuit (100) may also be based onthe BBJC A (101) and BBJC B (102) having the same doping type sequencep-n-p-n. Further, although the misalignment (302) represents same amountof misalignments for both the p-type and n-type regions, the p-typeregion and the n-type region may have a different amount ofmisalignment.

FIG. 2.2 shows a side view of a BBJC Y (321) and a BBJC Z (322)according to the legend (310). In one or more embodiments of theinvention, the BBJC Y (321) and BBJC Z (322) correspond to the BBJC A(101) and BBJC B (102), respectively, depicted in FIGS. 1.1. and 1.2above. Accordingly, the BBJC Y (321) and BBJC Z (322) correspond to thecross section A (120) and the cross section B (121), respectively,depicted in FIG. 1.1 above. In particular, the BBJC Y (321) and BBJC Z(322), thus the BBJC A (101) and BBJC B (102), have different andopposite doping type sequences p-n-n-p and n-p-p-n. Accordingly, theAPNJ Y (330) and BPNJ Z (333) are disposed in the same direction, whileAPNJ Z (332) and BPNJ Y (331) are disposed in the same directionopposite to the direction of the APNJ Y (330) and BPNJ Z (333).

As shown in FIG. 2.2, the APNJ Y (330) and BPNJ Y (331) have oppositep-n junction directions denoted by the arrows of the p-n junction icons.The APNJ Y (330) and BPNJ Y (331) are electrically connected into a pnnpcomponent (361) via the contiguous n-type doped region. In other words,the contiguous n-type doped region is used to form a pnnp electricalconnection sequence. Further, the APNJ Z (332) and BPNJ Z (333) alsohave opposite p-n junction directions denoted by the arrows of the p-njunction icons. The APNJ Z (332) and BPNJ Z (333) are electricallyconnected into a pnnp component (362) via the metal bridges (227). Inother words, the metal bridges (227) is used to form a pnnp electricalconnection sequence. Correspondingly in FIGS. 1.1 and 1.2, the BBJC A(101) and BBJC B (102) have the same pnnp electrical connection sequencebut have the different and opposite doping type sequences p-n-n-p andn-p-p-n, respectively. In addition, the p-n junction A (104) and p-njunction D (107) are disposed in the same direction, while the p-njunction B (105) and p-n junction C (106) are disposed in the samedirection opposite to the direction of the p-n junction A (104) and p-njunction D (107).

Further as shown in FIG. 2.2, the electrode A (303), electrode B (304),waveguide A (311), waveguide B (312), division line (301), andmisalignment (302) respectively correspond to the electrode A, electrodeB, arm A (211), arm B (212), division line (301), and misalignment (302)depicted in FIG. 1.2 above. Further, the n-type overlap region (342) andp-type overlap region (341) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction A (104), asdepicted in FIG. 1.1 above. Similarly, the n-type overlap region (343)and p-type overlap region (344) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction B (105), asdepicted in FIG. 1.1 above. In addition, the n-type overlap region (345)and p-type overlap region (346) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction C (106), asdepicted in FIG. 1.1 above. Similarly, the n-type overlap region (348)and p-type overlap region (347) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction D (107), asdepicted in FIG. 1.1 above.

In the waveguide A (311), the optical mode interacts with a combinationof p-type region (341) and p-type region (346). In the waveguide B(312), the optical mode interacts with a combination of p-type region(344) and p-type region (347). Independent of the misalignment (302),the combination of p-type overlap region (341) and p-type overlap region(346) is substantially the same size (e.g., within 10% or otherpre-determined amount) as the combination of p-type overlap region (344)and p-type overlap region (347). In other words, the optical modeinteracts with same amount (e.g., within 10% or other pre-determinedamount) of p-type material on both the waveguide A (311) and waveguide B(312).

In the waveguide A (311), the optical mode interacts with a combinationof n-type region (342) and n-type region (345). In the waveguide B(312), the optical mode interacts with a combination of n-type region(343) and n-type region (348). Independent of the misalignment (302),the combination of n-type overlap region (342) and n-type overlap region(345) is substantially the same size (e.g., within 10% or otherpre-determined amount) as the combination of n-type overlap region (343)and n-type overlap region (348). In other words, the optical modeinteracts with same amount (e.g., within 10% or other pre-determinedamount) of n-type material on both the waveguide A (311) and waveguide B(312).

Accordingly, the combination of doping type sequences, electricalconnection sequences, and p-n junction directions of the APNJs and BPNJsreduces the imbalance of the modulation strength incurred in opticalarms A and B.

Although the description of FIG. 2.2 is based on the doping sequencesp-n-n-p and n-p-p-n for the BBJC Y (321) and BBJC Z (322), respectively,the balanced operation of the optoelectronic integrated circuit may alsobe based on the BBJC Y (321) and BBJC Z (322) having the doping typesequences n-p-p-n and p-n-n-p, respectively. Further, although themisalignment (302) represents same amount of misalignments for both thep-type and n-type regions, the p-type region and the n-type region mayhave a different amount of misalignment.

FIG. 2.3 shows a side view of a BBJC Y (321) and a BBJC W (323)according to the legend (310). In one or more embodiments of theinvention, the BBJC Y (321) and BBJC W (323) correspond to the BBJC A(101) and BBJC B (102), respectively, depicted in FIGS. 1.1. and 1.2above. Accordingly, the BBJC Y (321) and BBJC W (323) correspond to thecross section A (120) and the cross section B (121), respectively,depicted in FIG. 1.1 above. In particular, the BBJC Y (321) and BBJC W(323), thus the BBJC A (101) and BBJC B (102), have different andopposite doping type sequences p-n-n-p and n-p-p-n. Accordingly, theAPNJ Y (330) and BPNJ W (337) are disposed in the same direction, whileAPNJ W (336) and BPNJ Y (331) are disposed in the same directionopposite to the direction of the APNJ Y (330) and BPNJ W (337).

As shown in FIG. 2.3, the APNJ Y (330) and BPNJ Y (331) have oppositep-n junction directions denoted by the arrows of the p-n junction icons.The APNJ Y (330) and BPNJ Y (331) are electrically connected into a pnnpcomponent (361) via the contiguous n-type doped region. In other words,the contiguous n-type doped region is used to form a pnnp electricalconnection sequence. Further, the APNJ W (336) and BPNJ W (337) alsohave opposite p-n junction directions denoted by the arrows of the p-njunction icons. The APNJ W (336) and BPNJ W (337) are electricallyconnected into a nppn component (363) via the contiguous p-type dopedregion. In other words, the contiguous p-type doped region is used toform a nppn electrical connection sequence. The metal bridge (228)connects respective n-type doped regions of the nppn component (363) tothe electrode A (303) and electrode B (304). Correspondingly in FIGS.1.1 and 1.2, the BBJC A (101) and BBJC B (102) have the different andopposite electrical connection sequences and have the different andopposite doping type sequences. In addition, the p-n junction A (104)and p-n junction D (107) are disposed in the same direction, while thep-n junction B (105) and p-n junction C (106) are disposed in the samedirection opposite to the direction of the p-n junction A (104) and p-njunction D (107).

Further, as shown in FIG. 2.3, the electrode A (303), electrode B (304),waveguide A (311), waveguide B (312), division line (301), andmisalignment (302) respectively correspond to the electrode A, electrodeB, arm A (211), arm B (212), division line (301), and misalignment (302)depicted in FIG. 1.2 above. Further, the n-type overlap region (342) andp-type overlap region (341) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction A (104), asdepicted in FIG. 1.1 above. Similarly, the n-type overlap region (343)and p-type overlap region (344) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction B (105), asdepicted in FIG. 1.1 above. In addition, the n-type overlap region (349)and p-type overlap region (350) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction C (106), asdepicted in FIG. 1.1 above. Similarly, the n-type overlap region (352)and p-type overlap region (351) correspond to the two different-size andopposite-type overlap regions separated by the p-n junction D (107), asdepicted in FIG. 1.1 above.

In the waveguide A (311), the optical mode interacts with a combinationof p-type overlap region (341) and p-type overlap region (350). In thewaveguide B (312), the optical mode interacts with a combination ofp-type overlap region (344) and p-type overlap region (351). Independentof the misalignment (302), the combination of p-type overlap region(341) and p-type overlap region (350) is substantially the same size(e.g., within 10% or other pre-determined amount) as the combination ofp-type overlap region (344) and p-type overlap region (351). In otherwords, the optical mode interacts with same amount (e.g., within 10% orother pre-determined amount) of p-type material on both the waveguide A(311) and waveguide B (312).

In the waveguide A (311), the optical mode interacts with a combinationof n-type overlap region (342) and n-type overlap region (349). In thewaveguide B (312), the optical mode interacts with a combination ofn-type overlap region (343) and n-type overlap region (352). Independentof the misalignment (302), the combination of n-type overlap region(342) and n-type overlap region (349) is substantially the same size(e.g., within 10% or other pre-determined amount) as the combination ofn-type overlap region (343) and n-type overlap region (352). In otherwords, the optical mode interacts with same amount (e.g., within 10% orother pre-determined amount) of n-type material on both the waveguide A(311) and waveguide B (312).

Accordingly, the combination of doping type sequences, electricalconnection sequences, and p-n junction directions of the APNJs and BPNJsreduce the imbalance of the modulation strength incurred in optical armsA and B.

Although the description of FIG. 2.3 is based on the doping sequencesp-n-n-p and n-p-p-n for the BBJC Y (321) and BBJC W (323), respectively,the balanced operation of the optoelectronic integrated circuit may alsobe based on the BBJC Y (321) and BBJC W (323) having the doping typesequences n-p-p-n and p-n-n-p, respectively. Further, although themisalignment (302) represents same amount of misalignments for both thep-type and n-type regions, the p-type region and the n-type region mayhave different amount of misalignment.

FIG. 3 shows a method flowchart in accordance with one or moreembodiments. In one or more embodiments, the method may be used tofabricate the optoelectronic integrated circuit and/or the opticalmodulator circuit depicted in FIGS. 1.1 and 1.2 above. One or more stepsshown in FIG. 3 may be omitted, repeated, and/or performed in adifferent order among different embodiments of the invention.Accordingly, embodiments of the invention should not be consideredlimited to the specific number and arrangement of steps shown in FIG. 3.

Initially, in Step 311, a first BBJC and a second BBJC are formedconforming to a BBJC fabrication pattern. In particular, one or morelithographic masks are used to form the first BBJC and the second BBJCaccording to a same doping type sequence. Further, the one or morelithographic masks dispose a first APNJ and first BPNJ of the firstBBJC, and a second APNJ and second BPNJ of the second BBJC along a samedirection. Accordingly, the first BBJC and the second BBJC have the sameelectrical connection sequence (i.e., pnnp sequence or nppn sequence).

In Step 312, the first BBJC and second BBJC are replicated. In one ormore embodiments, the replicated BBJCs are disposed along one or morelinear sections.

In Step 313, a third BBJC and a fourth BBJC are formed conforming to theBBJC fabrication pattern. In particular, one or more lithographic masksare used to form the third BBJC and the fourth BBJC according todifferent (e.g., opposite) doping type sequences. Further, the one ormore lithographic masks dispose metal layer connections such that thethird BBJC and the fourth BBJC have the same electrical connectionsequence. In addition, the one or more lithographic masks dispose (i)the first APNJ and the second BPNJ along a first direction, and (ii) thefirst BPNJ and the second APNJ along a second direction opposite to thefirst direction.

In Step 314, the third BBJC and fourth BBJC are replicated. In one ormore embodiments, the replicated BBJCs are disposed along one or morelinear sections. In particular, the replicated third BBJCs haverespective APNJs along the first direction, while the replicated fourthBBJCs have respective APNJs along the second direction. In one or moreembodiments, the replicated third BBJCs and the replicated fourth BBJCsare disposed in the one or more linear sections based on apre-determined direction alternating sequence.

In Step 315, a fifth BBJC and a sixth BBJC are formed conforming to theBBJC fabrication pattern. In particular, one or more lithographic masksare used to form the fifth BBJC and the sixth BBJC according todifferent (e.g., opposite) doping type sequences. Further, the one ormore lithographic masks dispose metal layer connections such that thefifth BBJC and the sixth BBJC have different (e.g., opposite) electricalconnection sequence. In addition, the one or more lithographic masksdispose (i) the first APNJ and the second BPNJ along a first direction,and (ii) the first BPNJ and the second APNJ along a second directionopposite to the first direction.

In Step 316, the fifth BBJC and sixth BBJC are replicated. In one ormore embodiments, the replicated BBJCs are disposed along one or morelinear sections. In particular, the replicated fifth BBJCs haverespective APNJs along the first direction, while the replicated sixthBBJCs have respective APNJs along the second direction. In one or moreembodiments, the replicated fifth BBJCs and the replicated sixth BBJCsare disposed in the one or more linear sections based on apre-determined direction alternating sequence.

In Step 317, an optical component is formed conforming to an opticalcomponent fabrication pattern that superimposes the BBJC fabricationpattern. The optical component fabrication pattern and the BBJCfabrication pattern may be formed in any sequence during thefabrication. In particular, one or more lithographic masks are used toform the optical component that (i) overlaps the aforementioned APNJs todefine a first p-type overlap region and a first n-type overlap region,and (ii) overlaps the aforementioned BPNJs to define a second p-typeoverlap region and a second n-type overlap region. In one or moreembodiments, the first p-type overlap region and the second p-typeregion are substantially same size (e.g., within 10% or otherpre-determined amount) independent of a fabrication misalignment amountof the BBJC fabrication pattern with respect to the optical componentfabrication pattern. In one or more embodiments, the first n-typeoverlap region and the second n-type region are substantially same size(e.g., within 10% or other pre-determined amount) independent of thefabrication misalignment amount of the BBJC fabrication pattern withrespect to the optical component fabrication pattern. Accordingly, therespective directions of the APNJs and BPNJs reduce an imbalance in theoptical component's interaction with the APNJs and BPNJs due to thefabrication misalignment.

As noted above, one or more of the Steps 311-316 may be omitted. Inother words, different combinations of the BBJCs depicted in FIGS.2.1-2.3 may be formed using the one or more lithographic masks. In oneor more embodiments, the Steps 311-316 may be performed simultaneouslyusing the same one or more lithographic masks.\

FIGS. 4-11 show examples in accordance with one or more embodiments ofthe invention. The examples shown in FIGS. 4-11 implement an opticalmodulator, such as a Mach-Zehnder (MZ) modulator, based on thefabrication pattern diagrams and method flow chart discussed inreference to FIGS. 1.1-1.2, 2.1-2.3, and 3 above. In particular, thecomponents depicted in FIGS. 4-11 according to legend (400) are examplesof the like-named components depicted in FIGS. 1.1-1.2 and 2.1-2.3above. Although not explicitly shown in FIGS. 4-11, RF termination isconnected at the end of the transmission line (electrodes A and B). Inone or more embodiments, one or more of the modules and elements shownin FIGS. 4-11 may be omitted, repeated, and/or substituted. Accordingly,embodiments of the invention should not be considered limited to thespecific arrangements of modules shown in FIGS. 4-11.

FIG. 4 shows the fabrication pattern of a MZ modulator based on the BBJCX (324) and pnnp component (364) depicted in FIG. 2.1 above. Inparticular, the APNJs and BPNJs of the MZ modulator are physicallyoriented along the same direction in the two waveguide arms. Forexample, the p-n junctions of the BBJC X (324) are physically laid outin a n-p-n-p doping type sequence while being electrically connected asa pnnp component. Connections between the APNJs and BPNJs, andconnections between the p-n junctions and the RF traveling-waveelectrodes may be realized using on-chip metal layers and contact vias.As the n-type overlap regions shift by substantially the same amount(e.g., within 10% or other pre-determined amount) for both waveguidearms under a misalignment of the fabrication masks, both arms havesubstantially the same size (e.g., within 10% or other pre-determinedamount) n-type overlap regions from all BBJCs as a group. Similarly, asthe p-type overlap regions shift by substantially the same amount (e.g.,within 10% or other pre-determined amount) for both waveguide arms underthe misalignment, both arms have substantially the same size (e.g.,within 10% or other pre-determined amount) p-type overlap regions fromall BBJCs as a group.

FIG. 5 shows the fabrication pattern of a MZ modulator similar to FIG. 4with the exception that the p-n junctions of each BBJC are physicallylaid out in a p-n-p-n doping type sequence while being electricallyconnected as a nppn component.

FIG. 6 shows the fabrication pattern of a MZ modulator based on the BBJCY (321), BBJC Z (322), pnnp component (361), and pnnp component (362)depicted in FIG. 2.2 above. In particular, the p-n junction's directionin the different segments changes along the length of each modulatingarm. For example, the p-n junctions of the BBJC Y (321) are physicallylaid out in a p-n-n-p doping type sequence and electrically connected asa pnnp component. In this context, the BBJC Y (321) is referred to as anon-inverted segment. In contrast, the p-n junctions of the BBJC Z (322)are physically laid out in an n-p-p-n doping type sequence while beingelectrically connected as a pnnp component. In this context, the BBJC Z(322) is referred to as an inverted segment. Accordingly, the opticalsignal propagates in the p-n junctions oriented in one direction (e.g.,the BBJC Y (321) of the non-inverted segment) over half of the arm'slength, and propagates in the p-n junctions oriented in the oppositedirection (e.g., the BBJC Z (322) of the inverted segment) over theremaining half. As a result of the opposite directions, the effectinduced by the misalignment in a non-inverted segment is compensated byan opposite effect induced in a corresponding inverted segment.

As shown in FIG. 6, the p-type region of each top diode (diodeoverlapped by the top arm) is connected to the electrode A for both thenon-inverted and inverted segments, and the p-type region of each bottomdiode (diode overlapped by the bottom arm) is connected to the electrodeB for both the non-inverted and inverted segments. The MZ modulator mayalso be implemented using nppn BBJCs where the n-type region of each topdiode is connected to the electrode A for both the non-inverted andinverted segments, and the n-type region of each bottom diode isconnected to the electrode B for both the non-inverted and invertedsegments.

FIG. 7 shows the fabrication pattern of a MZ modulator based on the BBJCY (321), BBJC W (323), pnnp component (361), and nppn component (363)depicted in FIG. 2.3 above. In particular, the p-n junction's directionin the different segments changes along the length of each modulatingarm. For example, the p-n junctions of the BBJC Y (321) are physicallylaid out in a p-n-n-p doping type sequence and electrically connected asa pnnp component. In this context, the BBJC Y (321) is referred to as anon-inverted segment. In contrast, the p-n junctions of the BBJC W (323)are physically laid out in a n-p-p-n doping type sequence while beingelectrically connected as a nppn component. In this context, the BBJC W(323) is referred to as an inverted segment. Accordingly, the opticalsignal propagates in the p-n junctions oriented in one direction (e.g.,the BBJC Y (321) of the non-inverted segment) over half of the arm'slength, and propagates in the p-n junctions oriented in the oppositedirection (e.g., the BBJC W (323) of the inverted segment) over theremaining half. As a result of the opposite directions, the effectinduced by the misalignment in a non-inverted segment is compensated byan opposite effect induced in a corresponding inverted segment.

As shown in FIG. 7, for the non-inverted segments, the p-type region ofeach top diode (diode overlapped by the top arm) is connected to theelectrode A and the p-type region of each bottom diode (diode overlappedby the bottom arm) is connected to the electrode B. In contrast, for theinverted segments, the n-type region of each top diode (diode overlappedby the top arm) is connected to the electrode B and the n-type region ofeach bottom diode (diode overlapped by the bottom arm) is connected tothe electrode A. This is referred to as a hybrid pnnp/nppn SPPconfiguration. The MZ modulator may also be implemented using theopposite structure (i.e., hybrid nppn/pnnp SPP configuration). In thehybrid pnnp/nppn SPP configuration, the BBJC Y (321) is physically laidout in a p-n-n-p doping type sequence and electrically connected as apnnp component. In contrast, the BBJC W (323) is physically laid out ina n-p-p-n doping type sequence while being electrically connected as anppn component.

The hybrid pnnp/nppn or nppn/pnnp SPP configuration uses two biasvoltages (i.e., bias voltage A, bias voltage B) to polarize the p-njunctions to operate in the depletion mode (reverse bias operation). Theuse of separate bias voltages may be advantageous in providing anadditional parameter to optimize the modulator performances (e.g.,frequency response, phase modulation imbalance, etc.).

The hybrid pnnp/nppn or nppn/pnnp SPP configuration allows the diodes tobe connected in series using a common doped region (e.g., n-type regionfor the pnnp segments and p-type region for the nppn segments). Metallayers and contact vias may be used to make the required connections tothe proper doped regions and traveling-wave RF electrodes. Bias voltagesmay also be brought to polarize the p-n junctions using appropriatemetal layers and contact vias.

The hybrid pnnp/nppn or nppn/pnnp SPP configuration leads to a symmetricoperation around ground voltage, with the use of the differentialmodulating signal having a DC component of 0V and bias voltages.+−.Vbthat are symmetric around ground voltage.

The MZ modulators depicted in FIGS. 6 and 7 above achieve equal phasemodulation efficiency in the two MZ modulator arms by inverting half thep-n junctions along the length of the waveguide arms. The inverted andnon-inverted p-n junctions may be placed in any order (referred to asthe direction alternating sequence) along the waveguide arm's length.FIG. 8 shows the fabrication pattern of a variation of the opticalmodulator circuit depicted in FIGS. 6 and 7 above. As shown in FIG. 8,the non-inverted and inverted segments may be laid out in a differentdirection alternating sequence along the length of the waveguides ascompared to FIGS. 6 and 7 above. Also, there may be different number ofnon-inverted and inverted segments to achieve an imbalanced operation.The proportion may be set to any number based on the desired amount ofimbalance in the modulation efficiency of the two MZ modulator arms.Further, the bias voltage may be brought to the BBJC segments from anydirection depending on the physical layout consideration, such as shownin FIG. 9. Specifically, FIG. 9 shows an example of routing variation inthe bias voltages for the optical modulator circuit with the pnnp/nppnhybrid SPP.

FIG. 10 shows the fabrication pattern of an example two-section opticalmodulator circuit having multiple segments in each section according tolegend (400). In particular, the section 1 includes pnnp BBJCs and thedriver polarity is such that the top electrode is connected to the +Sterminal of the driver 1 while the bottom electrode is connected to the−S terminal of the driver 1. In the section 2, the direction of the p-njunctions is reversed (to cancel the impact of mask misalignment) fornppn BBJCs. In order to not to cancel the phase modulation imparted tothe optical signal in the section 1, the driver polarity for the driver2 is reversed. In other words, the top electrode in the section 2 isconnected to the −S terminal of the driver 2 and the bottom electrode isconnected to the +S terminal of the driver 2.

In the configuration described above, the driver polarity is adjusted tocancel the imbalance caused by p-n junction misalignments. Specifically,the top waveguide in section 1 remains the top waveguide in section 2 tocancel the imbalance caused by mask misalignment. FIG. 11 shows thefabrication pattern in a variation of FIG. 10 where the driver 2 isdisposed at the opposite side to the driver 1. In the variation, the topwaveguide in section 1 becomes the bottom waveguide in section 2. Tocancel the imbalance caused by mask misalignment, the p-n junctiondirection is maintained the same in both waveguides. In other words,both section 1 and section 2 use the pnnp SPP configuration. However, inorder not to cancel the phase modulation imparted to the optical signalin the section 1, the driver polarity for the driver 2 is reversed. Inother words, the top electrode is connected to the −S terminal of thedriver 2 and the bottom electrode is connected to the +S terminal of thedriver 2.

Although a RF traveling-wave electrode is described in the examples ofFIGS. 4-11 above, the invention may equally apply to a N-section opticalmodulator circuit driven by N drivers where each section may be based ona lumped element (e.g., an electrode with a single segment containingtwo p-n junctions in a SPP configuration). The p-n junction directionsover the optical waveguides and the connection of the SPP lumpedsegments to the drivers may be configured to cancel the imbalance in themodulation efficiency caused by mask alignment using the principlesdescribed above.

Although a reverse bias operation of the p-n junction is described inthe examples above, the invention may equally apply to the p-n junctionsin forward bias operation, such as used in forward conduction or incurrent injection.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. An optical modulator comprising: a first arm anda second arm of an optical component, each arm includes an arrangementwith an equal amount of p-doped material and an equal amount of n-dopedmaterial, wherein the arrangement of each arm is configured such thatmisalignment with a division line of p-n junctions overlapped by theoptical component, resulting from mask misalignment, causes a sameeffect in both arms; and each arm overlapping with a plurality ofsegments and electrodes connect to the plurality of segments forpush-pull operation of the first arm and the second arm.
 2. The opticalmodulator of claim 1, wherein the optical component comprises a patternof at least one of semiconductor, oxide, and metal formed on at leastone of a wafer, die, and chip that superimposes fabrication patterns ofthe plurality of segments.
 3. The optical modulator of claim 1, whereineach segment of the plurality of segments includes a p-n junctionoverlapped by a corresponding one of the first arm and the second arm.4. The optical modulator of claim 3, wherein each arm overlaps withmultiple p-n junctions resulting in each arm including the equal amountof p-doped material and the equal amount of the n-doped materialindependent of the misalignment of the multiple p-n junctions with thedivision line.
 5. The optical modulator of claim 3, whereincorresponding segments overlapped by the first arm and the second armrespectively are back-to-back junction components, the back-to-backjunction components including one of a pnnp and a nppn configuration. 6.The optical modulator of claim 5, wherein the back-to-back junctioncomponents are separated by a non-doped region.
 7. The optical modulatorof claim 1, wherein corresponding segments overlapped by the first armand the second arm respectively are back-to-back junction components. 8.An optical modulator circuit comprising: a plurality of p-n junctionsegments; and an optical component including a first arm and a secondarm overlapping with corresponding segments of the plurality of p-njunction segments, the optical component including an arrangement wherethe first arm and the second arm include an equal amount of p-dopedmaterial and an equal amount of n-doped material, wherein thearrangement is configured such that misalignment with a division line ofp-n junctions overlapped by the optical component, resulting from maskmisalignment, causes a same effect in both the first arm and the secondarm, wherein electrodes connect to the plurality of p-n junctionsegments for push-pull operation of the first arm and the second arm. 9.The optical modulator circuit of claim 8, wherein the optical componentcomprises a pattern of at least one of semiconductor, oxide, and metalformed on at least one of a wafer, die, and chip that superimposesfabrication patterns of the plurality of p-n junction segments.
 10. Theoptical modulator circuit of claim 8, wherein each segment of theplurality of p-n junction segments includes a p-n junction overlapped bya corresponding one of the first arm and the second arm.
 11. The opticalmodulator circuit of claim 10, wherein each arm overlaps with multiplep-n junctions resulting in each arm including the equal amount ofp-doped material and the equal amount of the n-doped materialindependent of the misalignment of the multiple p-n junctions with thedivision line.
 12. The optical modulator circuit of claim 10, whereincorresponding segments overlapped by the first arm and the second armrespectively are back-to-back junction components, the back-to-backjunction components including one of a pnnp and a nppn configuration.13. The optical modulator circuit of claim 12, wherein the back-to-backjunction components are separated by a non-doped region.
 14. The opticalmodulator circuit of claim 8, wherein corresponding segments overlappedby the first arm and the second arm respectively are back-to-backjunction components.
 15. A method for forming an optical modulatorcircuit comprising: forming a plurality of p-n junction segments toalign p-n junctions of the p-n junction segments with a division line;forming an optical component including a first arm and a second arm tooverlap with corresponding segments of the plurality of p-n junctionsegments, wherein the optical component is formed with an arrangementwhere the first arm and the second arm include an equal amount ofp-doped material and an equal amount of n-doped material, wherein thearrangement is configured such that misalignment with the division lineof the p-n junctions overlapped by the optical component, resulting frommask misalignment, causes a same effect in both the first arm and thesecond arm, wherein electrodes connect to the plurality of p-n junctionsegments for push-pull operation of the first arm and the second arm.16. The method of claim 15, wherein forming the optical componentincludes forming a pattern of at least one of semiconductor, oxide, andmetal formed on at least one of a wafer, die, and chip that superimposesfabrication patterns of the plurality of p-n junction segments.
 17. Themethod of claim 15, wherein each segment of the plurality of p-njunction segments includes a p-n junction overlapped by a correspondingone of the first arm and the second arm.
 18. The method of claim 17,wherein each arm is formed to overlap with multiple p-n junctionsresulting in each arm including the equal amount of p-doped material andthe equal amount of the n-doped material independent of the misalignmentof the multiple p-n junctions with the division line.
 19. The method ofclaim 17, wherein corresponding segments overlapped by the first arm andthe second arm respectively are formed as back-to-back junctioncomponents, the back-to-back junction components including one of a pnnpand a nppn configuration.
 20. The method of claim 19, wherein theback-to-back junction components are separated by a non-doped regionformed therebetween.